Apium graveolens is a plant species in the family Apiaceae. The species consists of several morphologically distinct botanical varieties, each of which is used for a different purpose. The most important types are celery or stalk celery, which is designated Apium graveolens L. dulce; celeriac or root celery, which is designated Apium graveolens var. rapaceum; and smallage or leaf celery, which is designated Apium graveolens var. secalinum. 
In celery or stalk celery (Apium graveolens L. dulce), the part that is consumed is the petiole of the leaf, which is greatly enlarged. The petiole or ‘stalk’ quality, which covers many aspects, is one of the most important characteristics in breeding new celery varieties. This is therefore also the main characteristic that distinguishes var. dulce from var. rapaceum and var. secalinum, which do not have the solid, firm, thick, and long petioles that characterize var. dulce. 
In certain areas a stalk celery type called ‘white celery’ is marketed. A lower amount of chlorophyll in the stalks renders characteristics to the crop which are greatly favored by a number of consumers. To produce ‘white celery’, common stalk celery is grown on ridges in the field. While the celery is growing, the stalks are blanched by covering them up with soil, called ‘earthing up’, to prevent chlorophyll from developing in the stalks through the direct influence of sunlight. The resulting celery plants have a much lighter green or whitish color, which is subsequently marketed as a premium crop, ‘white celery’.
Because of the intensive process that is necessary for obtaining ‘white celery’, as well as the additional cleaning that is required after harvest, the production of ‘white celery’ is very costly and labor intensive.
In other regions, such as in Italy, a type called ‘sedano bianco’ (white celery) is produced, of which the best known variety is called ‘Sedano Bianco di Sperlonga’, without covering up the stalks to protect them from direct sunlight. These stalks however are indeed naturally lighter green than common stalk celery, but certainly not white. The same holds for so-called ‘self-blanching’ celery, which also has a lighter green color than regular green stalk celery.
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